Advanced polyaxial locking hook and coupling element device for use with top loading rod fixation devices

ABSTRACT

A hook device for use with support rod implantation apparatus, having a rod receiving body polyaxially mounted to a blade portion such that the body may be polyaxially manuevered relative to the blade, for easy rod coupling. The blade portion has a semi-spherical head portion which sits above the lamina. The rod receiving portion is a separate coupling element having lower and upper portions. The lower portion is slotted and tapered, and has a semi-spherical interior chamber in which the semi-spherical head is initially polyaxially disposed. The upper portion has a pair of upwardly extending members, defining therebetween a channel for receiving the rod. The uppermost parts of the upwardly extending members include an threading for receiving a top locking nut. A locking ring is disposed about the coupling element, substantially below the side recess; the top of the coupling element being initially positioned above the lower ledge of the side recess such that the rod, when initially disposed therein, seats against the top surface of the locking ring. When the rod is in place, the top locking nut is tightened to provides a downward force onto the rod. The rod, in turn, applies a force against the locking ring to descend down the tapered lower portion, therein locking the semi-spherical head in the interior chamber of the coupling element, and locking it into position relative to the blade portion. In an alternative variation, a rod retaining sleeve may be provided between the locking ring and the nut.

CROSS-REFERENCE TO PRIOR APPLICATION

This invention is a continuation-in-part of co-pending application, U.S.Ser. No. 08/502,803, filed Jul. 14, 1995, entitled "A Polyaxial LockingScrew And Coupling Element Assembly For Use With Rod Fixation Apparatus"which is, in turn, a continuation-in-part of application U.S. Ser. No.08/502,285, entitled "An Advanced Polyaxial Locking Screw And CouplingElement Device For Use With Rod Fixation Apparatus" filed Jul. 13, 1995,now U.S. Pat. No. 5,549,680.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a polyaxial locking spinal fixationdevice. More particularly, the present invention relates to a hook andcoupling element assembly for attaching to the posterior lamina portionof the spine and for polyaxially receiving and holding securely a rod ofan implantation apparatus using same.

2. Discussion of the Prior Art

The bones and connective tissue of an adult human spinal column consistof an upper portion having more than 20 discrete bones, and a lowerportion which consists of the sacral bone and the coccygeal bodies. Thebones of the upper portion are generally similar in shape, as will bemore fully described hereinbelow with respect to FIGS. 1 and 2. Despitetheir similar shape, however, they do vary substantially in size inaccordance with their individual position along the column and are,therefore, anatomically categorized as being members of one of threeclassifications: cervical, thoracic, or lumbar. The cervical portion,which comprises the top of the spine, up to the base of the skull,includes the first 7 vertebrae. The intermediate 12 bones are thethoracic vertebrae, and connect to the 5 lumbar vertebrae.

These bones of the upper portion vary in size, but are each similarlycoupled to the next by a tri-joint complex. The tri-joint complexconsists of an anterior disc and the two posterior facet joints, theanterior discs of adjacent bones being cushioned by cartilage spacersreferred to as intervertebral discs. Referring now to FIGS. 1 and 2, topand side views of a typical vertebral body of the upper portion of thespinal column is shown. The spinal cord is housed in the central canal10, protected from the posterior side by a shell of bone called thelamina 12. The lamina 12 has three large protrusions, two of theseextend laterally from the side ends thereof and are referred to as thetransverse process 14. The third extends back and down from the centerof the lamina and is called the spinous process 16.

The anterior portion of the spine comprises a set of generallycylindrically shaped bones which are stacked one on top of the other.These portions of the vertebrae are referred to as the vertebral bodies20, and are each separated from the other by the intervertebral discs22. Pedicles 24 are bone bridges which couple the anterior vertebralbody 20 to the corresponding lamina 12 and posterior elements 14, 16.

The lower portion of the spinal column, which extends into the hipregion is primarily comprised of the sacral bone. This bone is unlikethe other bones of the spinal column, in both shape and size. In fact,at birth humans have five distinct sacral bones which begin to fusetogether during childhood, and by adulthood have fully combined. For thepurpose of describing this invention, however, the sacral bone shall bereferred to as distinct from the spinal column; the spinal column,therefore, comprising for the purposes of this description, only thecervical, thoracic, and lumbar vertebrae.

In its entirety, the spinal column is highly complex in that it housesand protects critical elements of the nervous system which haveinnumerable peripheral nerves and arterial and veinous bodies in closeproximity. In spite of these complexities, the spine is a highlyflexible structure, capable of a high degree of curvature and twistthrough a wide range of motion. Genetic or developmental irregularities,trauma, chronic stress, tumors, and disease, however, can result inspinal pathologies which either limit this range of motion, or whichthreaten the critical elements of the nervous system housed within thespinal column. A variety of systems have been disclosed in the art whichachieve this immobilization by implanting artificial assemblies in or onthe spinal column. These assemblies may be classified as anterior,posterior, or lateral implants. As the classification suggests, lateraland anterior assemblies are coupled to the anterior portion of thespine, which is the sequence of vertebral bodies. Posterior implants areattached to the back of the spinal column, generally by coupling to thepedicles via screws, or by means of hooks which attach under the laminaand entering into the central canal. In either case, the implantsgenerally comprise elongate support rod elements which are coupled tothe screws or hooks to immobilize several sequential vertebrae, forexample to hold them stable so that the adjacent bones may be fused withbone graft. The prior co-pending application, U.S. Ser. No. 08/803,entitled "A Polyaxial Locking Screw And Coupling Element Assembly ForUse With Rod Fixation Apparatus", of which this application is acontinuation-in-part, discloses novel devices which providesignificantly superior performance for such implants which comprisescrews for coupling to the pedicles. The present invention relates tocorresponding implant apparatus which utilize hooks.

Such hook and rod assemblies generally comprise a plurality of hookshaving rounded blade portions which are inserted posteriorly under thelamina between the transverse process and the spinous process, and upperbody portions to which the support rod is coupled. The rod extends alongthe axis of the spine, coupling to each of a plurality of hooks viareceiving portions of their bodies. The aligning influence of the rodforces the spine to which it is affixed, to conform to a more propershape.

It has been identified, however, that a considerable difficulty may beassociated with inserting hooks under sequential lamina along amisaligned curvature and simultaneously exactly positioning their rodreceiving portion such that they are aligned so that the rod can bepassed therethrough without distorting, tilting, rotating, or exertingundesired translational forces on the hooks. Correction of thisdifficulty requires the time consuming and difficult task of reshapingthe rods or repositioning the hooks, each of which is understood torequire considerably longer operating time, which is known to increasethe incidence of complications associated with surgery. Often suchalignments with such fixed body hooks cannot be satisfactorily achieved,and the entire instrumentationing effort has to be altered to utilizingscrews.

It is, therefore, the principal object of the present invention toprovide a lamina hook having a rod coupling body which provides apolyaxial freedom of implantation angulation with respect to rodreception.

In addition, it is an object of the present invention to provide such anassembly which comprises a reduced number of elements, and whichcorrespondingly provides for expeditious implantation.

Accordingly it is also an object of the present invention to provide anassembly which is reliable, durable, and provides long term fixationsupport.

Other objects of the present invention not explicitly stated will be setforth and will be more clearly understood in conjunction with thedescriptions of the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION

The preceding objects of the invention are achieved by the presentinvention which is a lamina hook having a polyaxial coupling body foruse with rod stabilization and immobilization systems in the spine. Moreparticularly, the hook comprises a curvate flat hook shaped bladeportion having a ball shaped head. The body of the device comprises aseparate coupling element mounted on the ball shaped (semi-spherical)head so that it is rotationally free prior to secure fixation of the rodthereto, and which is securely locked in a given angulation once the rodis received by the coupling element. The coupling element has agenerally cylindrical main body portion, a locking ring, a top lockingnut, and, optionally an external rod securing sleeve.

More particularly, the coupling element may be conceptually divided intoa lower socket portion, and a top support rod and nut receiving portion.The lower socket portion is designed with an interior chamber having anopening at the bottom of the coupling element. The interior chamber isprovided for receiving therein the head of the blade portion such thatthe blade and the coupling element are held together, but prior to thesecuring of the rod to the intermediate portion, the blade and couplingelement remain polyaxially mated so that each may swing and rotatefreely with respect to the other. The external surface of the socketportion includes at least one vertical slot which is provided so thatthe semi-spherical head, which has a major diameter which is larger thanthe opening in the bottom of the element may be received within the openvolume therein. The at least one slot resiliently expands to receive thehead and contracts into position once the head is fully inserted,therein inhibiting the head from being retracted.

The exterior of the lower portion of the coupling element, into whichthe head is inserted, tapers outward slightly toward the bottom of theelement, therein having a slightly wider bottom diameter than at the topof the lower portion. A locking ring, having a diameter equal to orgreater than the top of the lower portion, but less than the diameter ofthe bottom of the lower portion, is disposed initially about the top ofthe lower portion.

Subsequent to proper positioning of the blade portion of the hook underthe corresponding lamina, the coupling of the rod to the couplingelement (as set forth in more detail hereinbelow), and the setting ofthe proper angulation of the coupling element relative to the hook, thelocking ring may be forced by a sufficient application of pressuredownward along the exterior of the lower portion of the couplingelement. The locking ring therein applies an inward force against thewalls of the interior chamber, and the corresponding narrowing of thevertical slots thereof. Once fully driven downward the locking ringcauses the coupling element to be securely locked relative to the bladeportion of the hook.

The upper portion of the coupling element comprises a channel whereinthe rod is retained. More particularly, the top of the cylindrical bodyis divided into two upwardly extending members, defining therebetween avertical channel. The vertical channel extends down from the top of thecylindrical body to a position slightly above the lower portion, and isideally suited for receiving the rod. The locking ring on the lowerportion is initially positioned so that the upper annular surfacethereof extends vertically above the bottom of the channel, so that inits corresponding initial disposition within the channel, the supportrod seats on the locking ring.

On the external surface of the uppermost portions of the upwardlyextending members, the coupling element comprises a threading onto whicha locking nut may be rotationally provided. The bottom surface of thenut is designed to seat against the top of the support rod. Driving ofthe nut downward on the support rod causes it to translate downward onthe locking ring. The locking ring correspondingly translates down theoutside of the lower portion of the coupling element, ultimatelyapplying an inward radial force thereto, causing the at least one slottherein to close and for the head of the hook to be locked therewith.The rod, too, is then securely locked between the top of the lockingring and the nut and is thereby prevented from axial or rotationalmovement.

An optional external rod securing sleeve may be provided between the toplocking nut and the support rod, the rod securing sleeve having acurvate bottom surface which is ideally suited for cupping the rod fromabove. The external rod securing sleeve is generally cylindrical inshape, having a hollow center for sliding over the top of the couplingelement. The bottom of the sleeve includes two opposing downwardlyextending members; forming therebetween a second channel. The sleeve,therefore, has a conformation which resembles an upside down U-shape andcups the rod from above. Subsequent to the placement of the rod in thechannel, the rod securing sleeve is deposited on the coupling elementsuch that the rod is positioned within the vertically aligned slotstherein.

Subsequent to the placement of the sleeve on the coupling element, thetop locking nut is threaded downward such that the bottom surfacethereof seats against, and drive downward on, the top surface of thesleeve. As the rod securing sleeve descends, the rod is driven downward,causing the locking ring to descend along the exterior of the lowersection, crush locking the head of the hook to the interior chamber ofthe coupling element. In this variation, the support rod is securedbetween the top surface of the locking ring and the curved bottomsurface of the rod securing sleeve. Because the rod securing sleeve hasa curved bottom surface, designed to mate with the top of the rod, theapplication of a securing force on the rod is spread out over a greaterarea.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a vertebral bone characteristic of those of thecervical, thoracic, and lumbar spine;

FIG. 2 is a side view of sequentially aligned vertebral bones, such asare found in the cervical, thoracic, or lumbar spine;

FIG. 3 is a side cross-sectional view of a blade portion of the hook ofthe present invention, said blade portion having a semi-spherical ballhead;

FIG. 4 is a side view of the top loading polyaxial coupling element ofthe present invention;

FIG. 5 is a side cross-section view of the top locking nut of thepresent invention;

FIG. 6 is a side view of the locking ring of the present invention;

FIG. 7 is a side view of the coupling element of FIG. 4 wherein thelocking ring of FIG. 6 is disposed about the coupling element;

FIG. 8 is a fully assembled hook of the present invention shown with asupport rod secured therein; and

FIG. 9 is a side view of the optional rod securing sleeve of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While the present invention will be described more fully hereinafterwith reference to the accompanying drawings, in which particularembodiments are shown, it is to be understood at the outset that personsskilled in the art may modify the invention herein described whileachieving the functions and results of this invention. Accordingly, thedescriptions which follow are to be understood as illustrative andexemplary of specific structures, aspects and features within the broadscope of the present invention and not as limiting of such broad scope.

Referring now to FIG. 3, a side view of the blade portion 100 of thehook device is provided. The blade portion 100 comprises a head portion102 and a C-shaped portion 104. The lower extending branch 106 of theC-shaped portion 104 comprises a flat member which is understood to bethe portion which is inserted under the lamina of the patient's spine.The semi-spherical head portion 102 is connected to upper extendingbranch of the C-shaped portion 104 at a neck portion 108.

The head portion 102 of the blade portion comprises a semi-sphericalshape. It is understood that the semi-spherical shape is a section of asphere. In the embodiment shown, the section is greater in extent than ahemisphere, and it correspondingly exhibits an external contour which isequidistant from a center point of the head. In a preferred embodiment,the major cross-section of the semi-spherical head 102 includes at least270 degrees of a circle.

Referring now to FIG. 4, a first embodiment of the coupling element 200of the present invention is shown in a side view, wherein criticalfeatures of the interior of the element are shown in phantom. Thecoupling element 200 comprises a generally cylindrical body which may beconceptually separated into a lower portion 202, and an upper portion206, each of which shall be described more fully hereinbelow.

First, with respect to the lower portion 202, the exterior surface 208of the body is tapered in the elongate direction such that the body iswider at the bottom 210 of the lower portion 202 than at the top 212thereof. The bottom 210 of the element includes an expandable andcontractable opening 214, defined by annular lip 213, which forms themouth of an expandable and contractable interior chamber 216. Thediameter of the opening 214, when otherwise unaffected by externaldeflecting forces, is more narrow than the maximum diameter A--A of theinterior chamber 216. The interior chamber 216 has a generally curvateinner surface 218 which is correspondingly shaped to receive thesemi-spherical head 102 of the blade portion 100.

The exterior surface of the lower portion 202 includes a series of slots220 which extend vertically upward from the bottom 210 of the element toa point which is closer to the top 212 of the lower portion 202 than themaximum horizontal diameter A--A of the interior chamber. The slots 220are provided in order that the application of an external deflectingforce may widen or narrow the opening 214 therein permitting theinsertion of an object, such as the head 102 of the blade portion, whichis larger than the undeflected diameter of the opening 214, orconversely, providing for the retention of an object such as the same.

The upper portion 206 of the generally cylindrical body of the couplingelement 200 includes a large removed section which forms a verticalchannel 222 in the top of the coupling element 200. More particularly,the top of the generally cylindrical body is divided into two upwardlyextending members 204a, 204b, which define therebetween the channel 222.The rod receiving channel 222 further comprises a curvate bottom 224.The depth of the bottom 224 is established such that a support rod (seeFIG. 8) which is positioned in the rod receiving channel 222 may nestsfully within the coupling element 200.

The exterior surface of the uppermost part of the upwardly extendingmembers 204a, 204b having a threading 226 thereon. The threading 226 isideally suited for receiving a top locking nut (see FIG. 6). In theembodiment shown in FIG. 4, the vertical distance between the bottom 224of the channel 222 and the top of the coupling element is large enoughthat when the support rod is inserted therein, a top locking nut maystill be engaged on the threading 226 at the top of the upwardlyextending members 204a, 204b. The distance from the top of the couplingelement to the bottom of the channel is represented in FIG. 4 by lineB--B. This permits the rod to be translated vertically within thechannel 222 (the purpose for which is set forth herein below withrespect to FIGS. 6-9).

Referring now to FIGS. 5 and 6, a top locking nut 235 and the lockingring 230 of the first embodiment are shown in side cross-section views.Referring now to FIG. 6, the locking ring comprises a generallycylindrical body having an inner diameter which is substantially equalto the diameter of the upper portion 206 of the coupling element 200,such that it may be disposed about the coupling element (see FIGS. 7 and8) but is initially prevented from descending fully down onto thetapered lower portion 202. The upper annular surface 233 of the lockingring 230 further includes a pair of diametrically opposed notches 232(one of which is shown in the side view of FIG. 6) which is designed toreceive therein the support rod.

Referring now to FIG. 5, the nut 235 comprises an inner threading 236which is intended to mate with the threading 226 on the exterior surfaceof the upwardly extending members 204a, 204b, such that the nut 235 maybe rotationally translated downward about the upper portion 206 of thecoupling element. In the first variation, the bottom surface 238 of thenut 235 is intended to seat against the top of the support rod, but ispermitted to rotate relative to the sleeve, therein providing a meansfor driving the rod downward (as more fully described hereinbelow withrespect to the full assembly of the device, and with respect to FIG. 8).

Referring now to FIG. 7, the coupling element 200, as described morefully with respect to FIG. 4, is shown in a side view, wherein the head102 of the blade portion 100 has been received within the interiorchamber 216, and a locking ring 230 is shown in its pre-locked positionabout the top 212 of the lower portion 202. The head 102 is rotationallyfree to move relative to the coupling element 200, however, they areprevented from fully separating by the annular lip 213 at the bottom 210of the lower portion 202. The locking ring 230, as described above,comprises a contiguous annular element having an inner diameter which isequal to the outer diameter of the lower portion 202 at the top 212thereof. In order to lock the coupling element 200 relative to the bladeportion 100, therein eliminating the freedom of the coupling element 200to freely rotate or angulate on the ball head 102, the locking ring 230must be forced downward relative to the coupling element 200.

It shall be understood that a dowel, protuberance, or other suitablemeans may be provided at or above the top 212 of the lower portion 202so that the ring 230 may not be easily moved upward, and therebypreventing separation of the locking ring during handling prior to use.In addition, it shall be further understood that in its properlyinserted orientation, it is desirable for coupling element 200 to berotated approxiamtely 90 degrees relative to the blade portion 100 suchthat the channel 222 may receive therein a rod which is alignedsubstantially co-linearly with the lower branching portion 106 of theblade portion 100.

With reference now to FIG. 8, which shows a side view of the fullylocked coupling element, rod, and hook system, the preferred method ofimplantation and assembly is described hereinbelow. (It shall beunderstood that, as described with respect to FIG. 7, the desireddisposition of the coupling element 200, relative to the blade portion100 is rotated approximately 90 degrees from the view provided in FIG.8. More particularly, the coupling element 200, when properly implanted,is oriented relative to the blade portion such that the rod portion 250extends substantially co-linearly with the direction of the bladeportion.) First, the blade portion 100 is positioned on the lamina (notshown) such that the lower extending branch portion 106 thereof ispositioned under the lamina and in the spinal canal. It is critical thatthe lower extending branch portion 106 be positioned as close to flushagainst the lamina as possible.

The head 102 of the blade portion 100 is then inserted into the interiorchamber 216 of the coupling element 200. (This step may, of course, betaken prior to the positioning of the blade portion relative to thelamina.) At this point in the assembly process, the locking ring 230 hasnot yet been forced downward along the outwardly tapered lower portion202 (as shown in FIG. 7) thereby providing the coupling element 200 withthe capacity to rotate and angulate relative to the positioned bladeportion 100 one another. This permits the support rod 250 to be properlynested within the rod receiving channel 222.

Once the proper angulation of the coupling element to the blade portion100, and the secure nesting of the rod 250 within the receiving channel222, have been established, the top locking nut 235 is threaded onto thethreaded upwardly extending members 204a, 204b. The lower surface 238 ofthe nut 235 seats against the top the rod 250. As the nut 235 rotates,and descends relative to the coupling element, the rod is forced totranslate downward in the channel 222, causing the locking ring 230 totranslate downward along the lower portion 202 of the coupling element200. By descending along the tapered lower portion 202 of the element,the locking ring 230 provides an inwardly directed deflecting forcewhich causes the slots 220 in the lower portion 202 of the element tonarrow so that the ring may proceed downward. This deflection inwardcauses the inner surface 218 of the interior chamber 216 to crush lockagainst the head 102 of the blade portion 100. This clamping force locksthe angulation of the coupling element 200 relative to the blade portion100. Ultimately, once the locking ring 230 cannot be translated down anyfurther, the downward force of the nut 235 against rod 250 causes therod to be locked between the nut and the top surface 233 of the lockingring 230. This locking prevents the rod 250 from sliding relative to theassembled structure (along an axis which is perpendicular to the planeof FIG. 8). The full insertion of the top locking nut 235, therefore,locks the rod 250 to the coupling element 200, as well as the bladeportion 100 to the coupling element 200.

Referring now to FIG. 9, in an alternative variation a rod securingsleeve may be introduced between the top locking nut 235 and the supportrod 250. The rod securing sleeve 240 comprises a hollow cylindrical body244 having a flat annular top surface 242 and a curved bottom surface252. In fact, the bottom surface 252 is so curved as to have anupside-down U-shape defined by a pair of downwardly extending members253a, 253b formed of the cylindrical body 244. These downwardlyextending members 253a, 253b, in turn, define diametrically opposingvertical slots 246, which together provide a passage through the bottomof the sleeve for cupping a rod placed therethrough. The interiordiameter of the sleeve 240 is equal to the outer diameter of the upperportion 206 of the coupling element 200, so that it may be placedthereover. After the rod 250 is appropriately positioned, the rodsecuring sleeve 240 is dropped over the element, such that the rodextends outward through the diametrically opposed vertical slots 246 inthe sleeve 240. The subsequent application of the top locking nut 235onto the coupling element provides a downward force on the rod securingsleeve 240 and the rod 250, and in turn, on the locking ring 230. Thisforce causes the rod to translate downward, along with the locking ring230, thereby locking the semi-spherical head 102 in the interior chamber216 of the coupling element 200. In addition, the rod 250 is lockedbetween the bottom surface of the sleeve and the top surface of thelocking ring 230.

While there has been described and illustrated a single embodiment of alamina hook having a polyaxial coupling element body, it will beapparent to those skilled in the art that variations and modificationsare possible without deviating from the broad spirit and principle ofthe present invention. The present invention shall, therefore, belimited solely by the scope of the claims appended hereto.

We claim:
 1. A polyaxial hook assembly for use with orthopedic rodimplantation apparatus, comprising:a blade portion, having a curvedshape for cupping the lamina, a lower extending member for dispositionbeneath the lamina, and a semi-spherical head which is disposed abovethe lower extending member; a coupling element includingan expandableand contractable interior chamber in a lower portion thereof forreceiving therein said semi-spherical head, said interior chamberfurther having an expandable and contractable opening for receivingtherethrough said semi-spherical head, a pair of upwardly extendingmembers formed of an upper portion of the coupling element, defining arod receiving channel for receiving therein a support rod of saidorthopedic rod implantation apparatus, and a surface threading disposedon an uppermost exterior surface of said upwardly extending members; alocking ring mounted around said coupling element, the downwardtranslation of said ring providing a force which causes said interiorchamber and said opening thereof to contract, therein locking the bladeportion to the coupling element; and a top locking nut, mateable withsaid surface threading.
 2. The polyaxial hook assembly as set forth inclaim 1, wherein said coupling element further comprises at least onevertical slot extending upward from said opening, therein rendering saidinterior chamber and said opening expandable and contractable.
 3. Thepolyaxial hook assembly as set forth in claim 2, wherein a portion ofsaid coupling element which contains said interior chamber comprises anexterior surface taper, said portion being wider at said opening,whereby the downward translation of said locking ring causes theinterior chamber and said opening to contract.
 4. The polyaxial hookassembly of claim 3, wherein the assembly further comprises a rodsecuring sleeve, positionable about, and in rod securing relationshipwith, said rod receiving channel for securing said rod therein.
 5. Thepolyaxial hook assembly as set forth in claim 4, wherein a bottomsurface of said top locking nut seats against a top surface of said rodsecuring sleeve, and the support rod seats against a top surface of saidlocking ring, the downward translation of said top locking nut therebycausing said support rod to be crush locked between said rod securingsleeve and said locking ring.
 6. The polyaxial hook assembly as setforth in claim 5, wherein said downward translation of said nut on saidexterior threading of said coupling element causes the downwardtranslation of said locking ring to crush lock the semi-spherical headwithin said interior chamber.
 7. The polyaxial hook assembly as setforth in claim 3, wherein a bottom surface of said top locking nut seatsagainst a top surface of said rod, and a bottom surface of the rod seatsagainst a top surface of said locking ring, the downward translation ofsaid top locking nut thereby causing said support rod to be crush lockedbetween said rod securing sleeve and said locking ring.
 8. The polyaxialhook assembly as set forth in claim 7, wherein said downward translationof said nut causes the downward translation of said locking ring tocrush lock the semi-spherical head within said interior chamber.
 9. Apolyaxial hook assembly for use with orthopedic rod implantationapparatus, comprising:a blade portion, having a curved shape for cuppingthe lamina, a lower extending member for disposition beneath the lamina,and a semi-spherical head which is disposed above the lower extendingmember; a coupling element having lower and upper portions thereof, saidlower portion including a taper wherein the bottom of the portion iswider than the top, said coupling element includingat least one verticalslot formed in said lower portion extending upward from a bottom of saidlower portion, an opening in said bottom of said lower portion, forreceiving therethrough said semi-spherical head, said opening beingexpandable and contractable by via forces applied to said at least onevertical slot; an interior chamber disposed within said lower portion,for receiving therein said semi-spherical head, a pair of upwardlyextending members formed of the upper portion of said coupling element,defining therebetween a rod receiving channel for receiving therein asupport rod of said orthopedic rod implantation apparatus, and anexterior threading disposed on an uppermost exterior surface of saidupwardly extending members; a locking ring mounted around said lowerportion, the downward translation of said ring applying an inward forceto said at least one vertical slot and therein locking thesemi-spherical head within the coupling element; and a top locking nutwhich is mateable with said exterior threading.
 10. The polyaxial hookassembly as set forth in claim 9, further comprising a rod securingsleeve comprising a hollow cylindrical body, having a opposing verticalslots, said sleeve being positionable about said coupling element forsecuring said rod within said channel, wherein said rod passes throughsaid vertical slots of said sleeve.
 11. The polyaxial hook assembly asset forth in claim 10, wherein a bottom surface of said top locking nutseats against a top surface of said rod securing sleeve, the support rodseats on a top surface of the locking ring, and the downward translationof said top locking nut causes said support rod to be locked between abottom surface of the rod securing sleeve and the top surface of thelocking ring.
 12. The polyaxial hook assembly as set forth in claim 11,wherein the downward translation of said top locking nut on saidexterior threading of said upwardly extending members causes thedownward translation of the support rod within the channel, whichcorrespondingly causes the locking ring to descend and crush lock thesemi-spherical head within said interior chamber.
 13. The polyaxial hookassembly as set forth in claim 9, wherein a bottom surface of said toplocking nut seats against a top surface of said rod which in turn seatson a top surface of the locking ring, and the downward translation ofsaid top locking nut causes said support rod to be locked between thebottom surface of the top locking nut the top surface of the lockingring.
 14. The polyaxial hook assembly as set forth in claim 13, whereinthe downward translation of said top locking nut on said exteriorthreading of said upwardly extending members causes the downwardtranslation of the support rod within the channel, which correspondinglycauses the locking ring to descend and crush lock the semi-sphericalhead within said interior chamber.
 15. An orthopedic rod implantationapparatus, comprising:at least one elongate rod; a plurality ofpolyaxial hook assemblies for coupling said elongate rod to lamina of aspine, each of said hook assemblies includinga blade portion, having acurved shape for cupping the lamina, a lower extending member fordisposition beneath the lamina, and a semi-spherical head which isdisposed above the lower extending member; a coupling element having, anexpandable and contractable interior chamber for receiving therein saidsemi-spherical head, said interior chamber having an expandable andcontractable opening for receiving therethrough said semi-sphericalhead, a pair of upwardly extending members formed of an upper portion ofsaid coupling element, and defining therebetween a rod receiving channelfor receiving therein a rod of said orthopedic rod implantationapparatus, and a surface threading disposed on an uppermost exteriorportion of said upwardly extending members; a locking ring mountedaround said coupling element, the downward translation of said ringproviding a force which causes said interior chamber and said openingthereof to contract, therein locking the blade portion to the couplingelement; and a top locking nut, mateable with said surface threading.16. The apparatus as set forth in claim 15, wherein each of saidcoupling elements further comprises at least one vertical slot extendingupward from said opening, therein rendering said interior chamber andsaid opening expandable and contractable.
 17. The apparatus as set forthin claim 16, wherein a portion of said coupling element which containssaid interior chamber comprises an exterior surface taper, said portionbeing wider at said opening, whereby the downward translation of saidlocking ring causes the interior chamber and said opening to contract.18. The apparatus as set forth in claim 17, further comprising a rodsecuring sleeve, positionable about, and in rod securing relationshipwith, said rod receiving channel for securing said rod therein.
 19. Theapparatus as set forth in claim 18, wherein a bottom surface of said toplocking nut seats against a top surface of said rod securing sleeve, thesupport rod seats against a top surface of said locking ring, wherebythe downward translation of said top locking nut causes said support rodto be locked between a bottom surface of said rod securing sleeve andsaid top surface of said locking ring.
 20. The apparatus as set forth inclaim 19, wherein the downward translation of said top locking nut onsaid exterior threading of said upwardly extending members causes thedownward translation of said support rod within said channel, whichcauses the downward translation of the locking ring so as to crush lockthe semi-spherical head within said interior chamber.
 21. The apparatusas set forth in claim 17, wherein a bottom surface of said top lockingnut seats against a top surface of said rod, and a bottom surface ofsaid rod seats against a top surface of said locking ring, whereby thedownward translation of said top locking nut causes said support rod tobe locked between the bottom surface of said top locking nut and saidtop surface of said locking ring.
 22. The apparatus as set forth inclaim 21, wherein the downward translation of said top locking nut onsaid exterior threading of said upwardly extending members causes thedownward translation of said support rod with said channel, which causesthe downward translation of the locking ring so as to crush lock thesemi-spherical head within said interior chamber.